Skimming over lime rendered walls

[HelenR]

Hi,
I'm aware this may well open a can of worms and leave me more confused than I was before but it's worth a shot!

I've recently purchased an 1850's terraced house in Devon which needs quite a lot of work doing to it. The internal walls in the lounge and bedroom are in a horrible mess and have been hacked about by the plumbers when putting in the gas & central heating, and the electricians when re-wiring the house. Instead of getting each channel individually patched, I thought it would be simpler and have a better overall effect if I just got the 2 rooms fully re-skimmed.

I'm a bit of a DIY novice so didn't realize until I got some quotes for the skimming that my walls are actually lime rendered (over cob-type stuff). Only one of the four plasterers pointed this out and said that you couldn't use the modern gypsum plaster over this (cracks, damp, structural problems etc). I have since asked the other three plasterers and they said it would be absolutely fine, they've been doing it for the past 35+ years and have never had a problem. (One of these plasterers is an old family friend whom I have a lot of trust in).

I don't want to risk damp problems (the house is completely bone-dry, I've not seen an inch of damp so far) and likewise don't want to risk the new plaster cracking and falling off, but at the same time there is no way I can afford to get both rooms re-lime rendered.

What are my options? What are the chances of there actually being any serious long-term problems if I gypsum over the lime?

Thanks in advance

 

[vinn]

OP,
Gypsum and cob dont mix and match - ever.

What do you mean by "lime rendered"? Are you talking about hacking back to the "cob" or simply skimming over what you've got with a lime skim?
The simplest form of skim for going over your in-situ plaster would probably be "Limelite" finish plaster or a similar remedial skim.

I can see bricks and stone rubble & possibly blockwork in your pics so quite what you have in the way of "cob" is a bit fuzzy - can you post pics of the exterior elevation(s) that show "cob" and/or a pic showing the ground floor thickness of window or door reveals?

There are a number of other issues that you might like to be advised on eg. the possibly dangerous wiring, & possible hygroscopic penetration of soot from your flues.

 

[HelenR]

Hi Vinn,

Thanks for the reply. Apologies for my incorrect terminology - as I said, I'm a complete novice at this. I meant lime plaster not lime render.
I'd really rather not hack back to the cob, I'd ideally like to just skim over what is already there (with gypsum multi-finish or similar). Does the Limelite require any special technical skills (other than the standard plastering skills!) to apply or will most plasterers be happy working with this?
From what I've read, the biggest trouble with using "modern" plaster over traditional lime plaster is that it forms a water-tight seal so you can get damp etc in the wall, as well as hairline cracks forming (if it dries too quick?) - it sounds like Limelite will reduce these risks, if I understand correctly?

As for the other q's, I don't have any of those photos to hand right now (at work) - the house seems to have been made from a hotch-potch of materials but the internal walls are a mixture of mud and twigs between a wooden frame (you can sort of see it where the skirting was in the third photo). The ground floor external wall is around 900 mm deep.

Cheers

 

[vinn]

Limelite is a remedial powder esp for going over backings such as yours.
Its applied like any other skim.
Its expensive but there are cheaper Remedial plasters.

Come back later if you want and deal with the other items then.

 

[bernardgreen]

The Lime Centre at Winchester gave me a lot of advice and supplied the materials needed to repair ( in part rebuild ) walls in my 500 year old cottage.

http://www.thelimecentre.co.uk/advice.htm e-mail at [email protected]

other sources are available

 

[Sammy777]

I've been on a castle job in Oxford recently. And the plasterers there were using lime plaster.
If you can afford it, I'd go with it.
It's breathable, which means that moisture can escape through the walls. So you should continue having no damp.
The finish is slightly more textured than gypsum. Personally I prefer it but not everyone does.
We work a lot with Lime. Mainly hydraulic. But I Love the stuff. Can't fault a product we've been using for thousands of years

 

[Sammy777]

I'd go with your trusted friend though. 2 materials, probably shouldn't mix. Although I haven't tried it